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A068997
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Numbers n such that Sum_{d|n} d*mu(d) divides n.
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5
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1, 2, 4, 6, 8, 12, 16, 18, 20, 24, 32, 36, 40, 48, 54, 64, 72, 80, 84, 96, 100, 108, 120, 128, 144, 160, 162, 168, 192, 200, 216, 240, 252, 256, 272, 288, 312, 320, 324, 336, 360, 384, 400, 432, 440, 480, 486, 500, 504, 512, 544, 576, 588, 600, 624, 640, 648
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OFFSET
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1,2
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COMMENTS
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The only squarefree terms so far are a(1), a(2), and a(4). - Torlach Rush, Dec 04 2017
There is a surjective mapping from all even numbers not in this sequence to terms of the sequence. The first such is 10 to a(9). The next is 14,28,42 to a(19). All even numbers not in the sequence are divisors of some term in the sequence. - Torlach Rush, Dec 08 2017
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LINKS
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FORMULA
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MAPLE
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with(numtheory): A068997 := i->`if`(i mod phi(mul(j, j=factorset(i)))=0, i, NULL): seq(A068997(i), i=1..650); # Peter Luschny, Nov 02 2010
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MATHEMATICA
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Select[Range[650], Divisible[#, DivisorSum[#, # MoebiusMu[#] &]] &] (* Michael De Vlieger, Nov 20 2017 *)
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PROG
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(PARI) for(n=1, 1000, if(n%sumdiv(n, d, moebius(d)*d)==0, print1(n, ", ")))
(Haskell)
a068997 n = a068997_list !! (n - 1)
a068997_list = filter (\x -> mod x (a173557 x) == 0) [1..]
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CROSSREFS
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KEYWORD
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easy,nonn
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AUTHOR
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STATUS
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approved
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